Hello Stéphane,
If you want manual control you can try to move New_fingering_engraver from
Voice to Staff. The Y-position has to be tweaked manually (which would kind of
not work if the side-axis-interface is used).
It is somewhat of a hack, to get this done propery we’d need to create an
engraver that collects Fingeringevents and displays them in a column left to
the notes.
Also note that you can leave New_fingering_engraver with Voice and do a
\temporary\override Staff.Fingering.stencil = ##f
To hide the double Fingerings. Then if you need the hack you can do a
\temporary\override Voice.Fingering.stencil = ##f
\revert Staff.Fingering.stencil
And when you’re done you can change back
\temporary\override Staff.Fingering.stencil = ##f
\revert Voice.Fingering.stencil
Cheers,
Valentin